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  Cooling rates of pyroclastic deposits inferred from mineral magnetic investigations: a case study from the Pleistocene Mýtina Maar (Czech Republic)

Lied, P., Kontny, A., Nowaczyk, N., Mrlina, J., Kämpf, H. (2020): Cooling rates of pyroclastic deposits inferred from mineral magnetic investigations: a case study from the Pleistocene Mýtina Maar (Czech Republic). - International Journal of Earth Sciences, 109, 1707-1725.
https://doi.org/10.1007/s00531-020-01865-1

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Item Permalink: https://gfzpublic.gfz-potsdam.de/pubman/item/item_5001956 Version Permalink: https://gfzpublic.gfz-potsdam.de/pubman/item/item_5001956_4
Genre: Journal Article

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Lied, Philipp1, Author
Kontny, Agnes1, Author
Nowaczyk, N.2, Author              
Mrlina, Jan1, Author
Kämpf, H.3, Author              
Affiliations:
1External Organizations, ou_persistent22              
24.3 Climate Dynamics and Landscape Evolution, 4.0 Geosystems, Departments, GFZ Publication Database, Deutsches GeoForschungsZentrum, ou_146046              
33.2 Organic Geochemistry, 3.0 Geochemistry, Departments, GFZ Publication Database, Deutsches GeoForschungsZentrum, ou_146041              

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Free keywords: Eger rift system · Maar-diatreme volcano · Titanomagnetite · Curie temperature · Cation ordering effect · Maghemitization · Pyroclastic emplacement mechanism
 Abstract: Tephra layers of the Mýtina Maar, Czech Republic, contain ferrimagnetic Mg–Al-rich titanomagnetite, which is suggested to originate from a fractionated alkaline CO2-rich lithospheric mantle melt. We investigated the magnetic mineralogy and Curie temperature (TC) from tephra deposits of two drill cores (< 9 m depth). TC calculated (208 ± 14 °C) from chemical composition (Fe2+0.8Mg0.5Fe3+1.1Al0.3Ti0.3O4) is in accordance with TC retrieved from cooling curves of temperature-dependent magnetic susceptibility measurements (195–232 °C). However, thermomagnetic curves are irreversible either with lower (type I) or higher (type II) TC in the heating curve. All curves show transition temperatures above ca. 390 °C, indicating maghemitization. We interpret the irreversibility of TC (∆TC) in terms of different degrees of cation ordering, overprinted or masked by different degrees of maghemitization, which is a low-temperature phenomenon. Negative ∆TC indicates that original deposited titanomagnetite has cooled faster and, therefore, has stored a lower degree of cation ordering compared to heating/cooling rate of 11 °C/min in the Kappabridge. Type II with positive ∆TC indicates higher degree of cation ordering, and, therefore, slower cooling rate. The central part of this deposit shows most severe maghemitization, indicating rather wet emplacement. We, therefore, suggest different eruption styles for deposition of type I pyroclastics with more phreatomagmatic and type II pyroclastics with more phreato-Strombolian eruption styles. Our study is a new approach to discriminate different cooling histories in maar deposits using the Curie temperature of titanomagnetite. We suggest that this method has the potential to discriminate different emplacement modes resulting from different eruption styles.

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 Dates: 2020-05-132020
 Publication Status: Finally published
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 Identifiers: DOI: 10.1007/s00531-020-01865-1
GFZPOF: p3 PT3 Earth Surface and Climate Interactions
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Title: International Journal of Earth Sciences
Source Genre: Journal, SCI, Scopus, p3
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Pages: - Volume / Issue: 109 Sequence Number: - Start / End Page: 1707 - 1725 Identifier: CoNE: https://gfzpublic.gfz-potsdam.de/cone/journals/resource/journals221